It is known that certain products, in particular food products, are impaired by oxygen and/or atmospheric humidity. They are therefore stored in an artificial atmosphere comprising a reduced oxygen and/or water vapour content.
For foods which are stored in flexible containers, a customary packaging method comprises evacuating the packaging containing the products and then sealing it gas-tight. This method is not possible in the case of containers having thin, in particular semirigid, walls, such as, for example, cans, cups or trays, since such containers do not as a rule withstand the forces which occur during evacuation.
Containers can be evacuated in a known manner in a vacuum chamber and then flushed with an inert gas, for example nitrogen. This multistage method requires a considerable outlay in terms of apparatus, energy and time. Only very sensitive and high-quality food products, such as, for example, milk powder, justify the use of such methods.
U.S. Pat. No. 2,519,353 discloses a sealing station for a filled tin can, in which a device for flushing the head space of the can with steam is integrated. The device has a flow channel for steam. It is formed by walls of the device and the can lid to be mounted on the can. The can lid is introduced into a hole in a wall of the channel. A controlled flow over the head space of the can from one side to the opposite side of the can opening is ensured through the channel. By means of such a flow, controlled gas exchange—without uncontrolled turbulence—takes place in the head space. Consequently, uniform evacuation of the air from the head space can be achieved. Air exchange carried out in this manner requires not only the closure element but also sealing of the can on the same station.
DE 3925952 C1 furthermore discloses a vessel sealing machine in which the filled glass bottles—driven by a continuously rotating turnstile—move around a circular path. The head space thereof is flushed with inert gas and closed with a crown cork. The flow chambers through which the inert gas flows are formed by two parallel walls which are fastened to the turnstile. The lower and the upper wall each have a passage for the bottleneck or crown cork pushed into the chamber. This vessel sealing machine is suitable for the gassing and direct sealing of rapidly revolving, filled glass bottles.